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Tag: Polio

What is Polio?

Your absolute favorite AP Biology blogger, Bacterina, is releasing a 3 part Special Edition feature about the Poliovirus. Prepare to be amazed and intrigued about the deadly disease of Polio and the incredibly effective Polio vaccine. 


Both an article on the historical significance of Polio and another on the Polio vaccines allow us to see the background of Polio.Poliomyelitis or Polio as it is commonly known has existed in the world for 6000 years. Researchers know this from the discovery of Egyptian mummies with withered limbs. The disease is a life-threatening disease caused by the poliovirus. More recently Polio was an epidemic in the 20th century in the US and over the world occurring mainly in the 1940s and 1950s. But in the 1950s a vaccine was created and the rates started to decrease. Since May of 1988, the World Health Assembly strives to eradicate poliomyelitis and because of this, the cases of Polio have decreased by 99%. Now the World Health Organization has declared the regions of the Americas, Western Pacific, and Europe as polio-free. On the other hand, South-East Asia is not free of polio but is working to eradicate the disease. The most well-known case of Polio was when President Franklin Delano Roosevelt was paralyzed by Polio and remained in a wheelchair for most of his adult life. The President was only in his late 30s when he got polio. Most people who are paralyzed by Polio were confined to wheelchairs or iron lungs for the rest of their adult lives. 

A Child Infected with Paralytic Polio

A very informative article written by the CDC informs us of the symptoms of Polio, how it is transmitted, and how to prevent the disease. The articles share the information which is explained below. 


Initially, individuals infected with Polio experience flu-like symptoms where they have a sore throat, fever, nausea, fatigue, headache. These symptoms last for 2 to 5 days and eventually go away. A smaller amount of people infected with polio will have more serious symptoms like paraesthesia, Meningitis, or Paralysis commonly in the legs, arms, or both (.5 percent of people will experience this). Of those who have paralysis, 2/100 will die from the paralysis because the virus will paralyze key muscles that allow ourselves to breathe. Only people who have paralytic disease polio are considered to have poliomyelitis. 


Poliovirus is a very contagious disease and lives in an infected person’s throat and intestines. It is spread through person to person contact by either fecal matter or from droplets of a sneeze or cough (less common). A person can be infected with polio if they have feces on their hands or on other objects that eventually enter their mouths. After someone is infected they can spread the virus to other people from immediately to two weeks. The virus can infect others if it contaminates food and water that is later ingested. 


There are two vaccines that act as preventative measures against this disease. The inactivated poliovirus vaccine (IPV) is given by an injection into a patient’s arm or leg depending on their age. In the United States, this vaccine has been used widely since 2000. The other type of vaccine is an Oral poliovirus vaccine which is used all over the world. Many children who get the vaccine are protected from the disease with a success rate of 99 percent. There is currently no cure for poliovirus but there are ways to speed up recoveries like bed rest, pain medications, and a ventilator.

Types of Polio Vaccines Available and How They Work

According to a very informative article by the Children’s Hospital of Philadelphia, there are two types of Polio Vaccines. Below we look at the specifics of these two vaccines.  

What types of Polio Vaccines are available? 

There are two types of Polio Vaccines the inactivated polio vaccine (IPV) and the oral polio vaccine (OPV). The IPV was made first in 1955 and is administered by a shot. The OPV which was made in 1961 is more convenient and is given by liquid form. These vaccines have been incredibly effective and have eradicated Polio in the US since 1979 and the Western Hemisphere since 1991. IPV is the only polio vaccine that is used in the US. 

How Were the Vaccines Made Initially?

Oral Polio Vaccine

The OPV was created from weakening three strains of the poliovirus that caused the disease by growing these strains in monkey kidney cells. Because this was growing the kidney cells the virus was able to be weakened where if ingested it would create an immune response that didn’t cause the disease. The OPV allows the body to have a first defense against the disease because the induced antibodies are in the intestines. But OPV rarely went back to the natural form which eventually caused paralysis. 

Inactivated Polio Vaccine 

The IPV, unlike the OPV, could not reproduce by itself which means that it does not have the capability to revert back to its natural form. In order to make IPV, the poliovirus is purified and killed with formaldehyde. Also unlike the oral vaccine, the IPV does not create antibodies in the intestines but rather in the bloodstream. This prevents the virus from traveling through the blood into the brain or spinal cord which then disables paralysis. 

Why does the US use only the Inactivated Polio Vaccine?

We only use the Inactivated Polio Vaccine instead of the Oral Polio Vaccine because the IPV cannot replicate which means it will never revert back to the natural form and cause paralysis. Now every infant in the US is required to have four doses of the shot. On the other hand countries outside of the US still use the oral version because it is more affordable and easier to give which allows more people to receive the vaccine.

Polio vaccine dropped on to sugar lump for a child patient

How Poliovirus Infects Our Bodies

How polio Initially affects your body – 

According to an informative article by Khan Academy, Poliovirus typically enters the body through the nose and the mouth and will immediately start to infect the cells of the lining of the larynx. The virus will then travel to the intestines where it will begin to reproduce rapidly. After a week of being infected the virus will start to spread to your tonsils and other parts of the immune system. Gradually the poliovirus will break into the bloodstream where it then can be transported around your body. Most of the time the virus will be eradicated in the bloodstream or in the intestines but in some people, it can infect the Central Nervous System. If it reaches the CNS it will begin to replicate inside of the motor neurons and copy itself thousands of times. Then when it is ready it will kill the neurons and spread to even more uninfected cells. The disease will then fall into three classifications depending on where the neuronal damage is occurring. 

two children polio-stricken children attending physical therapy circa 1963

Three classifications of Polio

Spinal Polio 

This is the classification when the poliovirus kills the motor neurons in the gray matter of the ventral horn of the spinal column. As the cells in the region are dying off the muscles of the limbs are not able to receive signals from the CNS so they begin to atrophy and become weak. In a few days, the patient will be fully paralyzed. This is the most common form of polio. 

Bulbar polio 

This form of polio is not as common as spinal polio. It is classified by this when the poliovirus infects and kills neurons in the bulbar region of the brain stem. This affects the muscles we use to speak, swallow, and breathe. 

Bulbospinal Polio

About 20 percent of people will get bulbospinal polio where they have both bulbar and spinal infection. In this situation poliovirus infects the upper part of the cervical spinal cord making the diaphragm paralyzed.   


Structure of Polio –     

An article by Science Direct and the American Society for Microbiology explains the structure of Poliovirus. Poliovirus is characterized as a nonenveloped virus and is composed of an RNA genome and a protein capsid. The genome is a single-stranded RNA genome and is 7500 nucleotides long. The shape of the virus is an icosahedral capsid and it belongs to the Picornaviridae family. Because poliovirus is a nonenveloped they don’t follow the same pathways as enveloped viruses take. Usually, with an enveloped virus the virus will deliver nucleocapsids to the cytoplasm of cells and fuse with the viral membrane with the host cell membrane. Instead, nonenveloped viruses will need to travel within the organelle membranes and infect specific cellular structures that would support the arrival of a virus to the cytosol. This is made possible when the virus penetrates across the endomembrane of the host cell which allows the virus to infect the cell. 

Type 3 poliovirus capsid, colored per chains

XRN1: The Virus Hitman

When I think of the words killer and assassin, my mind drifts to shady men in all black equipped with sniper rifles. However, recent research conducted by the University of Idaho and the University of Colorado Boulder has indicated that I should expand that mental list to include XRN1, a gene in saccharomyces cerevisiae which, according to a recent study, kills viruses within the yeast. Upon stumbling onto this subject, I was intrigued because it was a fairly simple procedure that led to a huge discovery. To grasp the significance of such a discovery, one must understand it on a molecular level. XRN1’s duty in yeasts is to create a protein which breaks down old RNA. The image below shows the generic process of the creation of a new protein through gene regulation.

Wikipedia- Regulation of Gene Expression

Wikipedia- Regulation of Gene Expression

Yeasts also contain viral RNA since practically all yeasts are infected by viruses. When scientists removed XRN1 from the yeasts, the viruses within yeasts replicated much faster, and when they expressed high amounts of XRN1, the virus was completely eradicated. This is because the XRN1 gene was inadvertently breaking down the viral RNA, mistakenly taking it for the yeast’s RNA. Scientists continued the research by using XRN1 from other saccharomyces yeast species. The virus continued replicating rapidly but the XRN1 did continue its job of breaking down the yeast’s RNA. This shows that the XRN1 from each yeast species evolves to attack the specific viruses that occur in its host while still maintaining their basic role as the RNA eaters. Scientists are hopeful about this study’s human health implications. Viruses such as Polio and Hepatitis C work by degrading XRN1 and not allowing it to break down RNA, respectively. Dengue Fever also occurs when XRN1 is unable to perform its function of RNA breakdown. These studies on Dengue Fever and Hepatitis C elaborate on the implications of XRN1 not breaking down RNA. Scientists hope that this discovery could lead to the triumph of XRN1 over these viruses. Could this really be the discovery that leads to the first ever Hepatitis C vaccine? Do you think that XRN1’s success against virus in yeasts guarantees eventual success against viruses in humans?


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